Single cycle transmitter

ABSTRACT

A single cycle transmitter at low and very low frequencies operates with an electrically short antenna. The transmitter produces an extremely short pulse of approximately one cycle duration. In response to a trigger signal, the transmitter&#39;&#39;s thyratron directly switches the antenna driving voltage, producing the first half cycle of a radiation pulse. The second half cycle is produced when diodes conduct. During this time, the thyratron deionizes, cutting off radiation.

United States Patent [191 Lewis et a1.

[ 1 SINGLE CYCLE TRANSMITTER [75] inventors: Edward A. Lewis, Harvard;John E. Rasmussen, Concord, both of Mass; James R. Stah1mann, Miramar,Fla.

[73] Assignee: The United States of America as represented by theSecretary of the Air Force, Washington, DC.

22 Filed: Dec. 15, 1972 21 Appl. No.: 315,745

[52] US. Cl 325/128, 325/162, 325/164, 325/169, 325/178, 325/186,343/701 [51] Int. Cl. H04b 1/04 [58] Field of Search.... 315/346, 352,356; 325/104, 325/105,125,l28, 120,121,141,161,162, 164, 166, 168, 169,185, 186; 343/701 1 Feb. 12, 1974 [56] Referenees Cited UNITED STATESPATENTS 3,659,203 4/1972 Rssn 325/105 Primary Examiner-Albert J. Mayer57 ABSTRACT A single cycle transmitter at low and very low frequenciesoperates with an electrically short antenna. The transmitter produces anextremely short pulse of approximately one cycle duration. In responseto a trigger signal, the transmitters thyratron directly switches theantenna driving voltage, producing the first half cycle of a'radiationpulse. The second half cycle is produced when diodes conduct. Duringthis time, the thyratron deionizes', cutting off radiation.

2 Claims, 4 Drawing Figures ,5: H/Gf/ VdLT/ME Paws .surmy TIP/6G ERl/VP/JT' 5002c:

SINGLE CYCLE TRANSMITTER BACKGROUND OF THE INVENTION SUMMARY OF THEINVENTION A single cycle VLF, LF transmitter is provided which isdesigned to operate with an electrically short antenna. The transmitterincludes a thyratron which in response to a trigger signal directlyswitches an extremely high DC antenna drive voltage to produce the firsthalf cycle of a radiation pulse. The second half cycle is produced whena solid state high voltage diode conducts. During this time thethyratron deionizes, cut ting off the radiation.

DESCRIPTION OF THE DRAWINGS FIG. I shows in schematic form the basicembodiment for the single cycle transmitter;

FIG. 2 shows a typical waveform of the current from the antenna terminalof FIG. 1;

FIG. 3 shows the waveform of the transverse magnetic field at a distanceof kilometers from the transmitter; and

FIG. 4 shows a second schematic circuit of the single cycle transmitterof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring in detailto FIG. 1, there is shown the basic embodiment of the VLF, LF singlecycle transmitter for pulsing electrically short antenna 10. 48 KV DChigh voltage power supply 11 having a negative output connects to groundand a positive output which charges transmitting antenna 10 throughinductor l2 and diode 113. Antenna It) acts somewhat like an open endedsection of a lossy transmission line, but the circuit may be understoodby considering the antenna as a lumped capacitance C of about 6,000 pf(for an annal 10a. It is approximately one cycle of a sine wave, but thearea under the second half cycle isslightly less than that of the first,so that for each actuation antenna 10 loses some charge. However, thisis resupplied within 500 pisec by charge flowing through inductor 12from high voltage power supply ll'l. Because of inductance 12, thevoltage on the antenna 10 is about percent higher than the supplyvoltage. With antenna 10 charged to 60 KV, each actuation of thethyratron circuit consumes about 2 joules. For a 1.5 km antenna, thetotal radiated energy is estimated at 0.35 joule per actuation. Whenoperated at 400 actuations per second the total radiated power is I40watts, with a power consumption of 1,500 watts, resulting in an overallefficiency of about 10 percent for the basic transmitter. Of the totalpower consumed, 700 watts is used by the thyratron heaters. FIG. 3 showsthe waveform of the trans verse magnetic field at a distance of IS kmfrom the transmitter observed with a loop antenna resistively loaded toflatten the response.

FIG. 4 shows a second schematic circuit for a single cycle transmitterwhich is basically identical in structenna 1.5 Km long). Thyratron 15 isprovided. It has control grid 15a, plate 15b, and cathode 150. When atrigger voltage from trigger input voltage source pulse generator 14 isapplied to grid 15a of hydrogen thyratron 15, the charge flows fromantenna 10 through inductance l9 (about 20 mh) for a time t 1r VLC 35,usec. The lumped capacitance C then has its maximum negative charge,thyratron 15 ceases to conduct, and charge flows back into antenna 10through now conducting diode 18 for an additional 35 usec, at which timethe lumped capacitance C is recharged positively. The system remains inthis condition until thyratron 15 is triggered again. If the length ofantenna 10 is reduced without charging inductance 19, the capacitance Cis reduced and the transmitted pulse' is of shorter duration and smalleramplitude. FIG. 2 shows a typical waveform of the current from antennatermiture and operation to that illustrated in FIG. I. 50 KV highvoltage supply 21 charges transmitting antenna 20 through charginginductor 22 and diode 23. Diode 23 consists of six high voltage diodesin series. Antenna 20 also has a fixed lumped capacitance C,. Antenna 20is associated with tuning inductor 29. Tuning inductor 29 includes taps29a 29d. Switch 31 selectively connects antenna 20 to the appropriatetape for antenna tuning purposes.

There is provided a pair of hydrogen thyratrons 2S and 25a operatinginconjunction to handle more effectively the voltage required. Isolationtransformers 26 and 26a provide the heater and :reservoir voltages tothyratrons 25 and 25a, respectively. Adjustable resistors 32 and 32a areutilized for control of the reservoir voltages of thyratrons 2S and 250,respectively. Resistors 33-38 conventionally utilized in associationwith thyratrons 25 and 25a to provide the proper operatingvoltages.Series arrangement of capacitor 39 and resistor 40 is inparallel arrangement with diode 28. A trigger voltage of 2,000 voltsof 2user; duration is supplied from trigger source 24 to thyratrons 25 and25a by way of isolation pulse transformers 27 and 27a, respectively.When the aforesaid'trigger is applied to thyratrons 25 and 25a, thecharge flows from the antenna through the inductance for a timehereinbefore described. The lumped capacitance C of antenna 20 then hasits maximum negative charge, the thyratrons cease to conduct, and chargeflows back through diode 28 for an additional time substantiallyequivalent to the first named time, at which time lumped capacitance C,is recharged positively. The system remains in this condition until thethyratrons are triggered again.

What is claimed is:

I. A very high power single cycle transmitter at low and very lowfrequencies comprising electrically short antenna means for low and verylow frequencies, said antenna means having a predetermined lumped capacitance, first inductance means having a preselected magnitude, firstdiode means in a series arrangement with said first inductance means, avery high voltage power source having a positive and negativeoutput,with said negative output connected to ground, said positive outputbeing connected to said antenna means by way of said series arrangementto charge said andiode means connected between said second inductanceand ground becoming conductive upon the cessation of conduction in saidthyratron means thus permitting a charge to flow back into said antennameans for a period substantially identicalto said preselected time,completing the second half of said single cycle at which time saidlumped capacitance is recharged positively.

2. A very high power single cycle transmitter as described in claim 1wherein said trigger means is comprised of a pulse generator.

1. A very high power single cycle transmitter at low and very lowfrequencies comprising electrically short antenna means for low and verylow frequencies, said antenna means having a predetermined lumpedcapacitance, first inductance means having a preselected magnitude,first diode means in a series arrangement with said first inductancemeans, a very high voltage power source having a positive and negativeoutput, with said negative output connected to ground, said positiveoutput being connected to said antenna means by way of said seriesarrangement to charge said antenna means, thyratron means having acathode, control grid, and plate, said cathode beIng connected toground, second inductance means having a preselected magnitude, saidsecond inductance means interconnecting said antenna means and saidplate of said thyratron means, means to trigger said thyratron means topermit the antenna charge to flow for a preselected time as determinedby the magnitude of said lumped capacitance and said second inductanceto complete a half cycle of said single cycle, said lumped capacitancethen having its maximum negative charge whereupon said thyratron meansceases to conduct, and second diode means connected between said secondinductance and ground becoming conductive upon the cessation ofconduction in said thyratron means thus permitting a charge to flow backinto said antenna means for a period substantially identical to saidpreselected time, completing the second half of said single cycle atwhich time said lumped capacitance is recharged positively.
 2. A veryhigh power single cycle transmitter as described in claim 1 wherein saidtrigger means is comprised of a pulse generator.